On many issues, little is known about Roberts' views. But in a 2003 opinion, he expressed a view held dear by many conservatives: that the reach of federal power under the Commerce Clause of the Constitution should be strictly limited.
In that case, Rancho Viejo v. Norton, Roberts suggested that the federal government overstepped its constitutional authority by applying the Endangered Species Act to protect the habitat of a toad that is indigenous to California.
Proponents of Oregon's assisted suicide law say Roberts' reasoning in the Rancho Viejo dissent should lead him to their view. They say their argument in favor of assisted suicide is essentially the same -- that the federal government has no authority to interfere in an issue reserved to state and local authorities and that affects only the citizens of one state.
"Hopefully, if he is willing to pre-empt the government's right under the Endangered Species Act to protect wildlife, then he would rule similarly in this case," said Rep. Peter DeFazio, D-Ore.
President Bush on Tuesday (July 19) picked Roberts, a judge on the U.S. Circuit Court of Appeals for the District of Columbia, to replace retiring Justice Sandra Day O'Connor, who was often the pivotal fifth vote in controversial decisions. If confirmed, Roberts would ascend to the high court just as it takes up the Bush administration's challenge to Oregon's assisted suicide law.
The central question in the Oregon case is whether the federal Controlled Substances Act can be used to prevent doctors from prescribing lethal doses of painkilling drugs to patients who are terminally ill.
Former U.S. Attorney General John Ashcroft challenged the Oregon law in 2001. He asserted that assisted suicide was not considered a "legitimate use" of controlled drugs and that doctors could be prosecuted under federal drug laws.
But lower courts so far have come down on the side of the Oregon law. They have held that Congress had no intention of regulating medical practice when it passed the drug law.
"This is not a case that requires a swing vote to win," said Eli Stutsman, a Portland, Ore., lawyer who has defended the law. "We are dealing with something that appeals to conservatives for reasons having to do with federalism."
Roberts' view of a limited federal government is shared by many at the highest levels of the Bush administration. But on some issues, that view can conflict with the values of social conservatives, many of whom say the federal government should intervene when states fail to protect life.
Abortion is the most prominent example of such a potential conflict, and on that issue Roberts' personal views are murky. As a deputy solicitor general in the administration of President George H.W. Bush, he co-authored a brief that said Roe v. Wade, the landmark Supreme Court decision that legalized abortion, "was wrongly decided and should be overruled."
But at his 2003 confirmation hearing for the appeals court, he said, "Roe v. Wade is the settled law of the land. ... There's nothing in my personal views that would prevent me from fully and faithfully applying that precedent."
The Oregon assisted suicide law is another such a case, according to those who hope the Supreme Court will uphold the federal government's authority to override the state statute.
Richard Doerflinger of the U.S. Conference of Catholic Bishops declined to comment directly on Roberts' nomination. But he said it probably wouldn't have an impact on the case. "We were going to win anyway," he said.
Sen. Gordon Smith, R-Ore., the only member of the Oregon congressional delegation who has supported the administration's view, said speculation about the outcome of the case would not be made clearer with Roberts' appointment.
"At this point, I don't think anyone knows where the highest court will come down," Smith said.
Smith noted that prospects for the Oregon law could be clouded by a Supreme Court ruling last month that clamped down on state medical marijuana laws. The court decided 6-3 that state-sanctioned marijuana smokers could be punished under federal law, possibly indicating that states' rights ended with federal drug laws.
Sen. Ron Wyden, D-Ore., rejected that argument, saying marijuana is different because it's illegal.
"Apples and oranges both grow on trees, but they are not the same," Wyden said. "It's a very different matter."